1. Field of the Invention
The present invention relates to a waveguide-type optical switch for controlling a propagating direction of the light which is transmitted in a waveguide.
2. Description of the Related Art
There has been known a Y-branch structured waveguide-type optical switch as one of main devices for constituting an optical integrated circuit. The Y-branch structured waveguide-type optical switch was disclosed in the literature (a) entitled "Electronic Communication Society Technical Research Report OQE 83-87" in which the waveguide-type optical switch comprises electrodes for electrically asynchronously controlling a guide of each branched waveguide.
This waveguide-type optical switch will be described more in detail with reference to FIG. 9.
The waveguide-type optical switch comprises a substrate 11 formed of LiN.sub.b O.sub.3 having an coupling region on the surface C thereof, a waveguide 13, branched waveguides 15a and 15b branched from the waveguide 13 at a branching angle .theta. and electrodes 17 (hatched portion in FIG. 9) having a portion provided at the coupling region having a length l between the branching point P and the portion where the coupling intensity of the branched waveguides is sufficiently weakened. The electrodes 17 control a refractive index in the branched waveguides 15a and 15b.
The waveguide-type optical switch is characterized in that an ON-OFF digital operation is performed utilizing an optical power of the even mode which is concentrated at the branched waveguide 15a or 15b where the refractive index is enhanced without utilizing an interference effect. The waveguide-type optical switch is also characterized in sufficient tolerance for a fabrication condition and an operation condition.
However, if the drive voltage is suppressed to a low value according to the conventional waveguide-type optical switch, the branching angle .theta. should be small as disclosed in the literature (a). Accordingly, the length l of the electrode (refer to FIG. 9) where the coupling intensity of both the branched waveguides is effectively retained is naturally lengthened which generated the problem in that the entire length of the device (entire length of l in FIG. 9 (horizontal length)) is lengthened.